ヒト口腔へん平上皮癌細胞のオカだ酸誘導アポトーシスにおけるＦａｓレセプターおよびＦａｓリガンド発現の制御とｃａｓｐａｓｅ活性

Abstract

Fas receptor is a member of the tumor necrosis factor/nerve growth factor receptor superfamily. Binding of Fas ligand to Fas receptor leads to activation of the latter and the induction of intracellular signals that result in apoptotic cell death. In the previous studies, our group demonstrated that okadaic acid, protein phosphatase inhibitor, induced apoptosis in several cell lines including human oral squamous carcinoma cells. In the present study, RT-PCR and Western blot analysis were used to examine the expression of mRNA and proteins of Fas receptor and Fas ligand in human oral squamous carcinoma SCC-25 cells treated with okadaic acid. Expression of Fas receptor and Fas ligand mRNAs treated with okadaic acid was stimulated in dose- and time-dependent manners as judged by semiquantitative RT-PCR analysis, with the maximum expression level at 20 nM- and 8 h-treatment. Okadaic acid also stimulated the expression of Fas receptor and Fas ligand proteins in these cells in dose- and time-dependent manners as judged by Western blot analysis. These results indicate that the expression of Fas receptor and Fas ligand is negatively regulated by a protein phosphatase sensitive to okadaic acid. The activity of NF-κB was also stimulated by okadaic acid treatment indicating that expression of Fas receptor and Fas ligand system in SCC-25 cells is related in the activity of NF-κB.To investigate whether expression of Fas receptor and Fas ligand is involved in okadaic acid-induced apoptosis in SCC-25 cells, effects of okadaic acid on caspase-3 activities were examined. Caspase-3 activities increased after 12 h okadaic acid treatment and maximal activities were observed at 48 h treatment. Okadaic acid induced caspase-3 activities in a dose-dependent manner. Marked nuclear condensation and fragmentation of chromatin were observed in the okadaic acid-treated cells by using Hoechst 33342 staining and electron microscopic observation. Okadaic acid also induced DNA ladder formation in the treated cells with a time-dependent fashion from 12 h to 48 h. The present results indicate that the expression of Fas receptor and Fas ligand is involved in okadaic acid-induced apoptosis in SCC-25 cells. The present results also indicate that Fas receptor and Fas ligand system might regulate apoptosis in SCC-25 cells in an autocrine fashion.